Recognition of a pathogen avirulence (AVR) effector protein by a cognate plant resistance (R) protein triggers a set of immune responses that render the plant resistant. Pathogens can escape this so-called Effector-Triggered Immunity (ETI) by different mechanisms including the deletion or loss-of-function mutation of the AVR gene, the incorporation of point mutations that allow recognition to be evaded while maintaining virulence function, and the acquisition of new effectors that suppress AVR recognition. The Dothideomycete Leptosphaeria maculans, causal agent of oilseed rape stem canker, is one of the few fungal pathogens where suppression of ETI by an AVR effector has been demonstrated. Indeed, AvrLm4-7 suppresses Rlm3- and Rlm9- mediated resistance triggered by AvrLm3 and AvrLm5-9, respectively. The presence of AvrLm4-7 does not impede AvrLm3 and AvrLm5-9 expression, and the three AVR proteins do not appear to physically interact. To decipher the epistatic interaction between these L. maculans AVR effectors, we determined the crystal structure of AvrLm5-9 and obtained a 3D model of AvrLm3, based on the crystal structure of Ecp11-1, a homologous AVR effector candidate from Fulvia fulva. Despite a lack of sequence similarity, AvrLm5-9 and AvrLm3 are structural analogues of AvrLm4-7 (structure previously characterized). Structure-informed sequence database searches identified a larger number of putative structural analogues among L. maculans effector candidates, including the AVR effector AvrLmS-Lep2, all produced during the early stages of oilseed rape infection, as well as among effector candidates from other phytopathogenic fungi. These structural analogues are named LARS (for Leptosphaeria AviRulence and Suppressing) effectors. Remarkably, transformants of L. maculans expressing one of these structural analogues, Ecp11-1, triggered oilseed rape immunity in several genotypes carrying Rlm3. Furthermore, this resistance could be suppressed by AvrLm4-7. These results suggest that Ecp11-1 shares a common activity with AvrLm3 within the host plant which is detected by Rlm3, or that the Ecp11-1 structure is sufficiently close to that of AvrLm3 to be recognized by Rlm3.

中文翻译：

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一个新的结构保守的真菌效应子家族显示出与植物抗性蛋白的上位相互作用

同源植物抗性 (R) 蛋白对病原体无毒力 (AVR) 效应蛋白的识别触发了一组免疫反应，使植物具有抗性。病原体可以通过不同的机制逃避这种所谓的效应触发免疫 (ETI)，包括AVR基因的缺失或功能丧失突变，在保持毒力功能的同时允许逃避识别的点突变的结合，以及获得抑制 AVR 识别的新效应器。Dothideomycete Leptosphaeria maculans是油菜茎部溃疡病的致病因子，是少数已证实 AVR 效应器可抑制 ETI 的真菌病原体之一。实际上，AvrLm4-7 分别抑制了由 AvrLm3 和 AvrLm5-9 触发的 Rlm3 和 Rlm9 介导的抗性。AvrLm4-7的存在不会阻碍AvrLm3和AvrLm5-9的表达，并且这三种 AVR 蛋白似乎没有物理相互作用。为了破译这些L. maculans AVR 效应器之间的上位相互作用，我们确定了 AvrLm5-9 的晶体结构，并基于 Ecp11-1 的晶体结构获得了 AvrLm3 的 3D 模型，Ecp11-1 是来自Fulvia fulva的同源 AVR 效应器候选者. 尽管缺乏序列相似性，但 AvrLm5-9 和 AvrLm3 是 AvrLm4-7 的结构类似物（先前表征的结构）。结构信息序列数据库搜索在L. maculans效应器候选者中发现了大量推定的结构类似物，包括 AVR 效应器 AvrLmS-Lep2，所有这些都在油菜感染的早期阶段产生，以及来自其他植物病原真菌的效应器候选者. 这些结构类似物被命名为 LARS（Leptosphaeria AviRulence 和 Suppressing）效应器。值得注意的是，表达这些结构类似物之一 Ecp11-1 的L. maculans的转化子在携带Rlm3的几种基因型中引发了油菜免疫. 此外，这种抗性可以被 AvrLm4-7 抑制。这些结果表明，Ecp11-1 在宿主植物中与 AvrLm3 具有共同的活性，可被 Rlm3 检测到，或者 Ecp11-1 结构与 AvrLm3 的结构足够接近以被 Rlm3 识别。